KR101426826B1 - Variable Resistance Type Droop Control Appratus and the Method for Stand-alone Micro-grid - Google Patents

Abstract

The present invention relates to a droop control apparatus and method for a stand-alone DC micro-grid, and more particularly, to a droop control apparatus and method for a stand-alone DC micro-grid, By changing the equivalent resistance of the droop controller, the power balance of the microgrid is effectively controlled while reducing the burden on the energy storage device. Specifically, the energy storage device is divided into a normal mode and a low-power mode according to a charge state by using a droop control method. In the normal mode, the grid power is controlled differently according to a grid voltage, And can be controlled efficiently.

Description

Technical Field [0001] The present invention relates to a variable resistance type droop control apparatus and method for a stand-alone micro-grid,

The present invention relates to a control apparatus and method of a direct current (DC) micro-grid power network. More particularly, the present invention relates to a control device and method for effectively controlling a micro grid power network while reducing the burden on an energy storage device by applying a droop control method having a variable equivalent resistance value to control an energy storage device included in a micro grid power network .

Recently, the micro grid power grid, which is independent of the existing power grid, has been widely used in the island and remote areas of the country, along with the rise of the smart grid, by using distributed power sources such as wind power and solar power and energy storage devices. However, There is a problem that requires frequent maintenance.

The micro grid grid can be classified according to the connection method and the control method. According to the linking method, the AC microgrid connecting AC components and the DC micro grid connecting DC can be distinguished. The AC microgrid has the advantage of taking advantage of the existing distribution, but it causes synchronization, stability, and reactive power problems. DC microgrid, on the other hand, has no problems with synchronization, stability, and reactive power, and has the advantage of low system loss and cost because it does not require two-stage power conversion in linking the power produced by each power source. In particular, DC micro-grids are more efficient because the digital load, which has recently been rapidly increasing, requires a DC power source. Recently, attention has been focused on the DC micro-grid.

As a classification according to the control method, there is a method in which a central controller is first operated and the system is operated by measuring the amount of power of the components in real time. This method requires a sensor for measuring the amount of power and a communication network for transmitting the measured data to the central controller. However, in the case of using distributed power sources such as wind power generation and photovoltaic power generation, there is a problem in that the airflow can not be maintained due to the weather There is a disadvantage in that a prediction algorithm is required and the dependence on the communication is high. In addition, this method is suitable for grid-linked microgrid because operation algorithm depends on power trading and focuses on maintaining power balance of upper system.

Another control scheme is an autonomous control scheme in which each converter associated with each element of the microgrid power grid (distributed power, energy storage, etc.) performs control over the associated elements. This method is a method of smoothly operating the micro grid power network as a whole, while each of the connected elements controls the operation of itself independently to some extent. According to this method, since it does not require expensive communication system and it can manage autonomous demand with light operation algorithm but it can not transfer the state between devices, it causes an excessive burden on the energy storage device, which may shorten its life span and it is difficult to efficiently operate distributed power. There is a drawback that a circulating current can flow between the elements. However, this autonomous control scheme is suitable for a stand-alone micro grid grid operating independently of the grid because it does not need a high-speed communication network and does not need to use a climate prediction algorithm and a complicated control algorithm. Since the stand-alone micro grid is disconnected from the existing power grid and operates independently, maintaining power balance during operation is the most important factor and the reliability determining technique.

The autonomous control scheme has the advantage of not requiring a high-speed communication network, a climate prediction algorithm, and a complicated central control algorithm. However, it can cause problems such as generation of circulating current and degradation of lifetime due to excessive use of the energy storage device . Therefore, in the case of controlling the DC micro grid power network based on the autonomous control method, there is a need for a control method that can prevent the excessive burden of the energy storage device while suppressing the circulating current.

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a DC micro grid power grid control apparatus capable of suppressing a circulating current and improving the life of an energy storage device while controlling the DC micro grid power grid by an autonomous control method. The purpose of the method is to provide.

According to the present invention, a variable resistance type droop control device for a stand-alone micro-grid including at least one distributed power source and an energy storage device includes a voltage reference value Vdroop ) Comprises a droop controller of an energy storage device set by Equation (1) below to cause the energy storage device to supply power to the microgrid or adjust power balance of the microgrid by receiving power, The equivalent resistance (Rv) of the droop controller is characterized in that the resistance value is set differently according to the charged state of the energy storage device.

[Equation 1]

Where V _DROOP is the voltage control reference value, V _Rate is the rated voltage, Rv is the equivalent resistance, and I _ES is the output current of the energy storage device.

In accordance with another aspect of the present invention, there is provided a droop control method of a variable resistance type for a stand-alone micro-grid including at least one distributed power source and an energy storage device, The voltage reference value Vdroop of the micro grid is set by the following equation (1) so that the energy storage device supplies power to the microgrid or receives power to control the energy storage device to regulate the power balance of the microgrid , And an equivalent resistance (Rv) of the droop controller is set to have a different resistance value depending on the charged state of the energy storage device.

[Equation 1]

Where V _DROOP is the voltage control reference value, V _Rate is the rated voltage, Rv is the equivalent resistance, and I _ES is the output current of the energy storage device.

According to the droop control method of the variable resistance type for the DC micro-grid power grid according to the present invention, circulation current between the elements constituting the power grid is suppressed, the excessive use of the energy storage device is restricted to improve the service life, There is an advantage that reliability can be increased.

1 is a conceptual diagram of a stand-alone DC micro-grid power network according to an embodiment of the present invention.
Figure 2 is a block diagram of a droop controller
FIG. 3 is a graph showing a droop curve graph for illustrating the droplet control method of the energy storage device
4 is a conceptual diagram of the control of the energy storage device according to the state of charge
FIG. 5 is a flowchart showing the operation of the energy storage device according to the charging state and the grid voltage.

The present invention can be achieved by the following description. It is to be understood that the following description is of a preferred embodiment of the present invention, and the present invention is not limited thereto.

1 is a conceptual diagram of a stand-alone micro-grid power network according to an embodiment of the present invention. The independent microgrid power grid according to the present invention includes an energy storage unit (ES) 110, a load unit 210, a wind generator (WG) 310, a photovoltaic array (PV) , 410, and an engine generator (EG) 510, as needed. The power elements include respective power conversion converters 120, 220, 320, 420, 520 to perform the required power conversion between each power element and the DC grid.

The droop controller 130 of the energy storage device controls the power flow between the energy storage device 110 and the DC grid using a droop control technique to control the overall power balance of the DC grid. Also, a distributed power source (DS) such as a wind power generator, a photovoltaic array, or an engine generator is provided independently of each of the distributed controllers 330, 430, and 530 and supplies power to the micro grid.

The wind generator (WG) 310 of FIG. 1 generates power using wind power and supplies the generated power to the DC micro grid. A conventional wind turbine generator is a rotary generator based power generator, and since the output is AC, the power converter 320 connected to the wind turbine generator 310 converts the alternating current into direct current and supplies it to the DC grid. Wind turbines have variable output power depending on wind speed, typically using a maximum output point tracking method to obtain maximum output in a given weather situation.

To this end, the power conversion converter 320 connected to the wind power generator 310 performs maximum power point tracking (MPPT) control in order to maximize the output of the wind power generator which varies according to the wind speed, Can be converted and supplied to the DC grid. As a wind turbine generator, it is preferable to use a PMSG (permanent magnet synchronous generator) which is easy to connect to a DC grid and has a wide range of availability. When the current control is performed so that the angular velocity of the wind turbine is constant, the output coefficient of the blade becomes the maximum, so that the mechanical output can be maximized.

A photovoltaic array (PV) array 410 may use conventional photovoltaic devices that produce electrical energy from sunlight. The power conversion converter 420 connected to the solar array serves to convert the output of the solar array and supply it to the DC grid. In order to always obtain the maximum output from the solar array whose output varies depending on the irradiation amount and temperature, MPPT Maximum Power Point Tracking) control. In general, since the voltage level of the open state of the solar array is lower than the grid voltage, the solar power conversion converter 420 preferably uses a DC-DC converter having a boost function capable of raising the voltage. As an example of the step-up DC-DC converter, a boost converter can be used. When using the MPPT control method, it may be desirable to use a three-phase interleaved Boost DC-DC converter to reduce this current ripple because the output contains a ripple of a certain frequency . In addition, among the MPPT control techniques, the Perturbation & Observation technique is advantageous in that it can be implemented easily and stably.

The engine generator (EG) 510 of FIG. 1 receives a power command according to the DC grid voltage from the associated EG dispersion controller 530, and supplies appropriate power to the DC grid. The power conversion converter 520 of the engine generator converts the alternating-current engine generator output to direct current and supplies it to the grid. As the method of controlling the output of the engine generator, it is preferable to use the angular speed control method.

A load (load) 210 is a power element consuming power and consuming power from the micro grid. The power conversion converter 220 provided between the load and the grid converts the direct current grid voltage into a proper type of power required by the load to supply power to the load. Generally, there may be an AC load and a DC load in the load. In order to supply power to an AC load, a DC / AC inverter that converts the DC grid voltage to AC is converted into a desired AC load and supplied. For example, in the case of a household load, the load power conversion converter 220 can be converted into a single-phase 220V AC used in a household and supplied. In the case of a DC load such as a digital load, the DC voltage level can be converted and supplied to the DC grid through the DC-DC converter. In this way, the DC micro grid can be converted to a digital load that requires DC power without AC conversion process, so that it is possible to supply only the voltage level, which is advantageous in that loss, cost, and size can be reduced.

Next, an energy storage device (ES) 110 of FIG. 1 and its related configuration will be described. As described above, the wind turbine, the solar array, and the engine generator are distributed power supplies for power supply, and the load is a configuration for consuming power. The energy storage device 110 functions to adjust the power balance of the micro grid power grid while receiving or supplying the power when the balance between the power generated by these distributed power sources and the power consumed by the load is not balanced. As the energy storage device, an element usually used for energy storage can be used, and typical examples thereof include a battery and a fuel cell.

The power conversion converter 120 connected to the energy storage device 110 controls the power of the grid while performing bi-directional power conversion and power transfer functions between the DC grid voltage and the energy storage device. That is, since the energy storage device must supply power from the grid and store or supply the stored power to the grid, the power conversion converter 120 may be a bidirectional DC-DC converter capable of transmitting power in both directions between the grid and the energy storage device Is preferably used. In particular, batteries used mainly in energy storage devices require low harmonic content in the incoming current, and current ripple during charging and discharging affects the life of the battery. Therefore, a bidirectional three-phase interleaved DC-DC converter Bidirectional 3-phase interleaved DC-DC converter).

Next, a droop control method for a stand-alone microgrid according to the present invention will be described.

Since the stand-alone micro grid is disconnected from the existing grid, maintaining power balance during operation is the most important factor and determines the reliability. In the droop control method according to the present invention, the distributed power supplies and the energy storage devices each independently control the power, but the power balance is maintained without generating the circulating current by the droop control method.

For this purpose, the energy storage device uses the droop control method to control the grid voltage while suppressing the circulating current, and also sets the operation area according to the state of charge (SOC) of the energy storage device to consider the protection of the energy storage device do.

In order to describe the droop control method according to the present invention in detail, a droop control method of the power conversion converter 120 for the energy storage device for controlling the power of the grid will be described with reference to FIGS. 2 and 3, 4 and FIG. 5, an operation sequence of the energy storage device according to the present invention will be described. Hereinafter, a droop control method according to the present invention will be described. However, the droop control method can be applied not only to an energy storage device but also to distributed power sources.

2 to 5 and the related description, values of ± 5%, ± 3%, and the like are used for the grid voltage value for determining the operation mode for convenience of explanation, 85%, 400V for the rated value of the grid voltage, and 100%, 70%, and 10% for the charge / discharge power of the energy storage device. However, these values are used as examples according to the present invention The values are given as values that can maximize the effect. However, other values may be used depending on the design conditions.

It should also be noted that the description "5% of the grid voltage" in FIGS. 2 to 4 and related description refers to a 5% increase in the grid rated voltage (ie, 105% of the rated voltage) Means a 5% reduction in the rated voltage (ie 95% of the rated voltage). ± 3%, ± 1%, etc. can be understood in the same manner.

In the stand-alone DC micro-grid, which is one embodiment of the present invention, an autonomous control scheme that does not transmit and receive information between each power element is used. If the autonomous control method is used, each of the two or more power conversion converters is set to control the voltage (Vdc) of the DC grid. In the voltage control of each component, the error of the sensor, the error of the controller, A circulating current is inevitably generated. The circulating current is similar to the AC reactive power and is directly related to the loss of the entire system. Therefore, a control method for suppressing the circulating current is necessary because it can adversely affect the equipment to be connected.

Since the circulating current is caused by the difference in the output voltage of each distributed power source operating as a voltage source, a method of easily reducing the circulating current is to insert an actual resistance between the output terminal of each distributed power source and the DC grid. However, this method is impractical in terms of loss, cost, and size.

2, a feedback loop for changing the voltage reference value V _DROOP by feeding back the output current I _ES to the controller 131 for controlling the output voltage of the power conversion converter 120 for the energy storage device (Droop control). That is, the output DC current I _ES is detected and multiplied by the gain Rv 132, and the result is subtracted from the original output voltage target value V _Rate to generate a modified voltage target value V _DROOP . The difference between the corrected target value V _DROOP and the actual output voltage Vdc is generated by a compensator 133 such as a PI or the like and a current reference value I _{ES_REF} is generated. So that the grid voltage Vdc, which is the output voltage finally, follows the corrected voltage reference value V _DROOP .

Since the grid voltage Vdc will follow V _DROOP by the function of the controller as described above, the grid voltage Vdc can be expressed by Equation (1).

[Equation 1]

Here, Rv serves as an equivalent resistance such that a resistor exists at the output terminal. That is, as the output current I _ES increases, the output voltage Vdc is reduced by a voltage corresponding to the voltage drop Rv I _ES of the resistor Rv. In this way, since the output voltage is formed as if there is a resistor even if there is no resistor, it can be seen that the circulating current generated by the difference of the output voltage with other converters can be suppressed by the equivalent resistor Rv.

Equivalent resistance Rv can be obtained by setting the magnitude of the desired voltage variation? V _dc according to the maximum output current value I _MAX of the energy storage device, (Equation 3) can be obtained by calculating this equivalent resistance on the basis of the resistance P _ES . That is, by setting the operation power value of the energy storage device and the voltage variation value at that time, an equivalent resistance can be obtained, and the operation power of the energy storage device can be adjusted by changing the equivalent resistance value.

&Quot; (2) "

&Quot; (3) "

Here, Rv is the equivalent resistance, △ V _dc output voltage fluctuation, I _ES by the equivalent resistance is the output current, V _dcmin is the minimum value of the output voltage, P _ES is the operating power of the energy storage device.

3 shows a droop curve for the DC grid voltage (Vdc) variation according to the current (I _ES ) of the energy storage device. The droop curve is divided into three areas (A, B, C) according to the voltage of the DC grid and the state of charge (SOC) of the energy storage device as shown in FIG. The A area controls the grid power using the energy storage device as the maximum power (100% for example) when the DC grid voltage is within a certain range (for example, -5% -3% and 3% -5% of the rated voltage) , And the equivalent resistance (R _{V - 100%} ) (first resistance value) at this time can be calculated in the same manner as in Equation (4). In the region of + 3% of the rated voltage, surplus power is introduced so that the energy storage device can receive the power at the maximum power. B region is a region where the DC grid voltage is 3% ~ 3% of the rated voltage and the grid power is controlled by setting the charge / discharge power of the energy storage device as normal power (70% for example) . Normal power usual to increase the life of the energy storage device is not the maximum power for charging an energy storage device, the discharge power is to manage the energy storage device to use only (e.g. 70%), wherein the equivalent resistance of the (R _{V_70%)} (Second resistance value) can be obtained as shown in the following equation (5). The C region is an over-charging and over-discharging protection region of the energy storage device, and when the state of charge (SOC) exceeds the predetermined operating range, the amount of electric energy for charging and discharging the energy storage device is sharply reduced to protect the energy storage device. The operating power at this time is the minimum power (for example, 10% power) and an example of the calculated equivalent resistance (R _{V - 10%} ) (third resistance value) is shown in Equation (6). As shown in FIG. 3, the slope of the droop curve changes in each region because the equivalent resistance Rv forming the droop curve changes as the power storage of the energy storage device changes.

&Quot; (4) "

&Quot; (5) "

&Quot; (6) "

Here, the values used in the equations (4) to (6) are calculated values, for example, with respect to the grid voltage, the variation value of the grid voltage and the capacity of the energy storage device, It goes without saying that the value can be varied.

In this way, the operating power of the energy storage device is divided into three levels according to the state of charge (SOC) and the grid voltage of the energy storage device, and the equivalent resistance Rv of the droop controller 130 is changed to give an excessive burden to the energy storage device The energy storage device can perform the power balance control function of the grid.

Next, the operation of the energy storage device in terms of the charging state of the energy storage device will be described with reference to FIG. The excessive charge or discharge of the energy storage device adversely affects the energy storage device life, so the energy storage device's state of charge (SOC) is an important factor to consider for reliability.

Use of the maximum value (MAX) and minimum value (MIN) in the SOC area of the energy storage device has a bad influence on the service life. 55% ~ 85%) to operate in normal mode. In this normal mode, control is performed at 70% or 100% power depending on the DC grid voltage. When the state of charge (SOC) of the energy storage device exceeds the predetermined high level or falls below the low level, the low power mode which converts the energy storage device capacity to 10% by adjusting the equivalent resistance of the energy storage device drupop control part according to the grid voltage (The influence of the grid voltage will be described with reference to FIG. 5). In the low power mode, when the charge state of the energy storage device enters the normal region again, it operates again in the normal mode. In FIG. 4, a 5% decrease value of High (95% of High value) and a 5% rise value of Low (105% of Low value) are used as a reference value for entering the normal mode in the low power mode, Hysteresis function is provided to prevent frequent switching between mode and low power mode.

5 is a view for explaining the operation sequence of the energy storage device according to the charge state (SOC) of the energy storage device and the grid voltage. In the present invention, in order to protect the energy storage device, when the charge state of the energy storage device is within a predetermined range, the normal power (for example, 70% or 100%) is set as the normal region (55% To perform a power balancing control sequence. If the grid voltage is within a certain range of the rated value (for example, -3% to +3%), the power management sequence in the case where the charged state of the energy storage device is in the normal region is 70% If the grid voltage deviates from a certain range of the rated value, the burden of the energy storage device is increased and the grid power is quickly controlled with 100% power.

If the charge state of the energy storage device exceeds the upper limit value (for example, 85%), it is in an overcharged state. In this case, in consideration of the grid voltage, the grid voltage is higher than the rated value, so that when the energy storage device is continuously charged, the load of the energy storage device is controlled by controlling the low power (for example, 10% If the device is overcharged but discharges, it will quickly discharge with normal power and regulate the power of the grid.

If the charge state of the energy storage device drops below the lower limit value (for example, 55%), it is overdischarged. In this case, considering the grid voltage, if the grid voltage is lower than the rated value, the energy storage device is in a state of continuously discharging, so that the load of the energy storage device is controlled by controlling the low power (for example, 10% power) When the storage device is charged, it operates with normal power and quickly charges the grid power.

In this way, by controlling the energy storage device in consideration of both the state of charge (SOC) of the energy storage device and the grid voltage, the load of the energy storage device can be reduced, and the grid power balance can be balanced. Here, the control of the charge power of the energy storage device to 100%, 70%, 10%, etc. is performed by changing the equivalent resistance Rv of the output terminal of the droop controller 130 for the energy storage device as described above .

Here, the values of the reference value of the charged state of the energy storage device, the reference value of the grid voltage, and the power of the energy storage device are selected as the values at which the protection of the energy storage device according to the present invention and the effect of grid power control can be maximized But it goes without saying that other values may be used depending on the type of energy storage device, the characteristics of the grid network, and the like. In addition, although the equivalent resistance is changed to three levels in consideration of both the charging state and the grid voltage of the energy storage device, the charging state of the energy storage device may be considered or the equivalent resistance may be changed in two steps The possibilities can be easily understood.

As described above, in the independent micro-grid, the energy storage device is controlled using the droop control method having variable resistance values in three stages based on the charge state (SOC) of the energy storage device and the grid voltage, It is possible to control the power balance of the microgrid while reducing the burden on the storage device. Specifically, when the charge state of the energy storage device is out of the normal range, the equivalent resistance of the droop controller is set to the maximum resistance value. If the charge state of the energy storage device is within the normal range, And is set to a minimum resistance value when the grid voltage is out of a certain range, thereby enabling the energy storage device to effectively control the grid power while reducing the burden on the energy storage device.

Although the droplet control method having the three-stage variable resistance value according to the charging state and the grid voltage has been described for the energy storage device, the distributed power sources (the wind power generator, the solar array, the engine generator, etc.) By applying the same principle and applying the droop control method having a variable resistance value according to the grid voltage, it is possible to control the grid power balance more efficiently by adjusting the power supplied to the grid according to the grid voltage.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be appreciated by those skilled in the art that numerous changes and modifications can be made. Accordingly, all such appropriate modifications and changes, and equivalents thereof, should be regarded as within the scope of the present invention.

110: Energy storage device (ES)
120: Power Conversion Converter for Energy Storage
130: ES droop controller
131: Voltage controller of the ES droop controller 132: Equivalent resistance
133: PI compensator of the voltage controller 210: Load
220: load power conversion converter 310: wind power generator (WG)
320: Power conversion converter for wind power generator 330: WG dispersion controller
410: Solar Array (PV)
420: Solar power conversion converter
430: PV dispersion controller 510: Engine generator (EG)
520: Power converter for engine generator 530: EG dispersion controller

Claims (10)

A variable resistance droop control device for a stand-alone microgrid comprising at least one or more distributed power sources and an energy storage device,
(Vdroop) of the controller of the energy storage device is set by the following equation (1) so that the energy storage device supplies power to the microgrid or receives power to adjust the power balance of the microgrid And a droop controller of the energy storage device,
The equivalent resistance (Rv) of the droop controller is set differently depending on the state of charge of the energy storage device,
The equivalent resistance (Rv) of the drop-
(a) if the charging state of the energy storage device is continuously charged in a state where the charging state is higher than a normal range, or if the charging state is continuously discharged in a state where the charging state is lower than the normal range,
In the case other than the case of (a) above,
(b) a second resistance value when the voltage control reference value is within a predetermined range,
(c) a third resistance value when the voltage control reference value is out of the predetermined range,
Wherein the first resistance value is the largest, the second resistance value is the medium value, and the third resistance value is set to be the smallest. The variable resistor type droop for the stand-alone microgrid droop control device.
[Equation 1]

Where V _DROOP is the voltage control reference value, V _Rate is the rated voltage, Rv is the equivalent resistance, and I _ES is the output current of the energy storage device.
The method according to claim 1,
The equivalent resistance Rv of the droop controller is set to be smaller than a resistance value when the charged state of the energy storage device is within the normal range and smaller than the resistance value when the charged state of the energy storage device is out of the normal range A variable resistance droop control device for a stand-alone micro-grid.
The method according to claim 1 or 2, wherein
Wherein the resistance value of the equivalent resistance Rv of the droop controller is set differently according to the voltage control reference value. The droop controller of the variable resistance type for the stand-alone micro-grid.
The method of claim 3,
The reason why the resistance value of the equivalent resistor Rv of the droop controller is set differently according to the voltage control reference value is that the resistance value when the voltage control reference value is within a certain range is smaller than the resistance value when the voltage control reference value is out of the predetermined range And the resistance value is set to be larger than a resistance value of the variable resistance type droplet control device.
delete A variable resistance droop control method for a stand-alone micro-grid including at least one or more distributed power sources and an energy storage device,
Wherein the droop controller of the energy storage device is configured such that a voltage reference value (Vdroop) of the controller is set by the following equation (1) so that the energy storage device supplies power to the microgrid or receives power, Control the energy storage device to regulate balance,
The equivalent resistance (Rv) of the droop controller is set differently depending on the state of charge of the energy storage device,
The equivalent resistance (Rv) of the drop-
(a) if the charging state of the energy storage device is continuously charged in a state where the charging state is higher than a normal range, or if the charging state is continuously discharged in a state where the charging state is lower than the normal range,
In the case other than the case of (a) above,
(b) a second resistance value when the voltage control reference value is within a predetermined range,
(c) a third resistance value when the voltage control reference value is out of the predetermined range,
Wherein the first resistance value is the largest, the second resistance value is the medium value, and the third resistance value is set to be the smallest. The variable resistor type droop for the stand-alone microgrid droop control method.
[Equation 1]

Where V _DROOP is the voltage control reference value, V _Rate is the rated voltage, Rv is the equivalent resistance, and I _ES is the output current of the energy storage device.
The method according to claim 6,
The equivalent resistance Rv of the droop controller is set to be smaller than a resistance value when the charged state of the energy storage device is within the normal range and smaller than the resistance value when the charged state of the energy storage device is out of the normal range A variable resistance droop control method for a stand-alone microgrid.
The method according to claim 6 or 7, wherein
Wherein the resistance value of the equivalent resistance Rv of the droop controller is set differently according to the voltage control reference value. The droplet control method for a stand-alone micro-grid according to claim 1,
9. The method of claim 8,
The reason why the resistance value of the equivalent resistor Rv of the droop controller is set differently according to the voltage control reference value is that the resistance value when the voltage control reference value is within a certain range is smaller than the resistance value when the voltage control reference value is out of the predetermined range And the resistance value is set to be larger than a resistance value of the variable resistor. delete

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